288 MORLEY R. KARE AND M. S. FICKEN 



been completed ; however, the response to dextrose, sucrose, maltose and 

 fructose suggests yet another pattern of response to the sugars. 



On the other hand, preference thresholds for some sugars in insects are 

 similar to those of the vertebrates (Prosser and Brown, 1961.) Perhaps this 

 convergence is related to similar selective pressures. Certainly substances 

 containing natural sugars are eaten by both insects and vertebrates, and 

 consequently natural selection could have favored responses to similar 

 concentrations in the two groups. 



1.0 10.0 100 



CONCENTRATION CMS/ 100 ML. 



Fig. 3. The response of the rat to various sugar solutions in a two-choice 

 preference test is illustrated. 



In an early paper on chickens (Kare et ai, 1957) a sHght preference for 

 sucrose was reported. Subsequently, in a more extensive study on sugars 

 (Kare and Medway, 1959), as was illustrated in Fig. 2, the chick was found 

 to be totally indifferent to sucrose and glucose solutions.* This contra- 

 dicted the marked preference for sugars by chicks reported by Jacobs and 

 Scott (1957). Assuming all the results were accurate, there were apparently 

 uncontrolled variables. 



The effect of a caloric deficiency on sugar preference in the chicken is 

 illustrated in Fig. 4 (Kare and Halpern, 1962). When fed, ad libitum, the 

 chick exhibited no preference for a 10 per cent sucrose solution where 

 distilled water was the alternative. However, where feed was limited to 

 75 per cent of that consumed by the controls, a preference for sucrose 

 solution became marked and in addition fluid intake almost doubled. 

 Evidently, the caloric needs of the animal lead to adaptive behavior. The 

 figure also indicates that animals which were initially on a restricted diet 

 continue at least for a time to show the same behavior, i.e., preference for 

 sucrose, after being placed on an adequate diet. It follows that it is 

 possible for a demonstrated preference for sugar to be related to a prior 



*This was in accordance with the results obtained by electrophysiological methods 

 (Kitchen et al., 1959). 



